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VectorMesonDecayMass.cpp
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VectorMesonDecayMass.cpp
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//==============================================================================
// VectorMesonDecayMass.cpp
//
// Copyright (C) 2021 Tobias Toll and Thomas Ullrich
//
// This file is part of Sartre.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation.
// This program is distributed in the hope that it will be useful,
// but without any warranty; without even the implied warranty of
// merchantability or fitness for a particular purpose. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//
// Author: Thomas Ullrich and Zhangbu Xu
// Last update:
// $Date: 2021-06-16 11:55:44 -0400 (Wed, 16 Jun 2021) $
// $Author: ullrich $
//==============================================================================
#include "VectorMesonDecayMass.h"
#include "EventGeneratorSettings.h"
#include <iostream>
using namespace std;
#define PR(x) cout << #x << " = " << (x) << endl;
double VectorMesonDecayMass::mass(int id)
{
double m;
switch (id) {
case 22: // DVCS
m = 0;
break;
case 113: // special for rho
m = rhoMass();
break;
default: // Breit-Wigner
m = bwMass(id);
break;
}
return m;
}
double VectorMesonDecayMass::bwMass(int id)
{
//
// Assuming Breit-Wigner line shape
//
Settings *settings = EventGeneratorSettings::instance();
TRandom3* rndm = settings->randomGenerator();
double m = settings->lookupPDG(id)->Mass();
double w = settings->lookupPDG(id)->Width();
double result = rndm->BreitWigner(m, w);
return result;
}
double VectorMesonDecayMass::rhoMass()
{
//
// rho line shape using STAR PRC 2017 parameters.
// omega interference term is neglected here.
// Code provided by Zhangbu Xu (BNL)
//
Settings *settings = EventGeneratorSettings::instance();
TRandom3* rndm = settings->randomGenerator();
double M0rho = 0.7765;
double Mpi = 0.139;
double W0rho = 0.156;
double Arho = 1.538;
double B2pi = -1.21;
double M2pi = 0.278;
double MaxSpectral = 1.1*(1.0/W0rho+pow(B2pi/Arho,2));
double Mrho = M0rho;
double Mspectral = 0.0;
while (Mspectral < rndm->Uniform(0.0,MaxSpectral)) {
Mrho = rndm->Uniform(M2pi,1.5);
double Wrho = W0rho*M0rho/Mrho*pow(((pow(Mrho,2)-4*pow(Mpi,2))/(pow(M0rho,2)-4*pow(Mpi,2))),1.5);
double PoleFactor = pow(Mrho*M0rho*Wrho,0.5)/(pow(Mrho*Mrho-M0rho*M0rho,2)+M0rho*M0rho*Wrho*Wrho);
Mspectral = pow((PoleFactor*(Mrho*Mrho-M0rho*M0rho)+B2pi/Arho),2)+pow(PoleFactor*Mrho*Wrho,2);
}
return Mrho;
}

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